Alternating current electrical discharge device



ALTERNATING CURRENT ELECTRICAL DISCHARGE DEVICE Filed March 7, 1930 HARLS SPRGZ'VH Smventoz Patented Jan. 16, 1934 ALTERNATING CURRENTELECTRICAL DISCHARGE DEVICE Charles Spaeth, Flushing, N. Y., assignor toNe-Arga Corporation, New York, N. Y., a corporation of New YorkApplication March '7, 1930. Serial No. 433,967

7 Claims.

This invention relates to electrical discharge devices of thealternating current type.

It is an object of my invention to provide a full wave electricaldischarge device which is adapted to operate efficiently for longperiods of time at high current density.

Another object is the provision of an electrical discharge device whichis so arranged and operated that an alkali metal electrode may be used 0at high current density without destructive sputtering effects.

In accordance with my invention an electrical discharge illuminatingtube is constructed with an elongated light transmitting gas filledenvelope having at one end a pair of electrode chambers and at the otherend a single cooperating electrode chamber. The electrodes of said pairof chambers are so arranged to be connected to a source of potentialsuch as a secondary of a trans former and are adapted to produceelectrons under the influence of normal exciting current. A connectionis made from an intermediate point of said source of potential, e. g.,an intermediate point of the secondary to the single electrode whichcooperates with said pair of electrodes. This single electrode may be ofalkali metal in order to reduce the potential drop thereof. In operationthe potential of the supply source is so selected that the pair ofelectrodes are ex cited by the currents passing between them,sufficiently to eject electrons. This insures that each of theseelectrodes in turn will act as a cathode in cooperation with the singleelectrode which then must necessarily be the anode. As

the anode fall of potential of all metallic materials is low thesputtering of the single electrode will be slight. However, an alkalimetal, which has a very small fall to potential when being used as ananode, may form the single electrode.

Where an alkali metal is so used, the sputtering is not suflicient tocoat the main light emitting portion of the envelope. For this reason,even when using an alkali metal in order to reduce the necessaryoperating potential of such an electrical discharge device, a normaldischarge current may be passed through the device many times as greatas that which may normally be successfully used with it, when the alkalimetal serves as a cathode. This is due to the fact that an anode fall ofpotential is only a small fraction of a cathode fall of potential of ametal.

The above mentioned and other objects and advantages of the device andmanner of obtaining them will be made clear in the following descriptionand accompanying drawing.

In the drawing, the figure illustrates a tube constructed in accordancewith my invention, and the operating circuit therefor.

Reference numeral 1 indicates an envelope or 69 tube of glass, quartz orother light transmitting material having a filling of rare gas, such asneon, at a pressure of a few millimeters of mercury. This envelope hasat one end a pair of electrode chambers 2 and 3 containing electrodes 4and 5 respectively. At the other end of the tube is a chamber 6containing an electrode '7 which is preferably of an alkali metal oralloy thereof, but which may be of any other ordinary material. Theelectrodes 4 and 5 preferably comprise a relatively thin sheet oftungsten which is adapted to be heated to incandescence by passage ofnormal discharge current therethrough. These electrode are of lowthermal capacity. Other electrode materials may be used in placethereof, provided they are adapted to produce electrons in normaloperating conditions. Connected to the envelope 1 at some suitablepoint, for example, adjacent the electrode chambers 2 and 3, is areservoir 8 containing a quantity of mercury 9. A tube 10 which projectswithin the reservoir prevents the mercury from entering the main portionof the envelope 1. Connected to the envelope 1 and projecting within theelectrode chamber 6 is a tube 11 of restricted diameter, the object ofwhich is to prevent particles sputtered from the surface of theelectrode 7 from entering the light emitting portion of the envelope 1.Adjacent to the pointof junction to this tube and the envelope 1 aplurality of small openings or breather holes 12 are made in the wall ofthe tube.

The circuit connections for the device comprise a transformer 13 havingits primary connected to a suitable source of potential 14 and havingits secondary 15 connected to the electrodes 4 and 5 through the usuallead-in wires.

A connectlon 16 is made from the mid point of the transformer secondarythrough a choke coil 17 and the lead-in wire to the electrode 7, andanother connection is made between one of the pair of electrodes, forexample, 5 and a lead-in wire of the mercury electrode 9. Thisconnection includes a variable resistance 18.

In operation the current supply source 14 is caused to energize theprimary of the transformer whereupon a potential is applied to theelectrodes 4 and 5 which causes a gaseous discharge current to passtherebetween. This discharge is sufiicient, because of the properproportioning of the potential of the transformer secondary with respectto the spacing between the electrodes and the pressure of the gas withinthe envelope, to cause electrodes 4 and 5 to become heated to the pointof incandescence. As soon as this point is reached the electrodes startradiating electrons. These electrodes are therefore thermionic. Adischarge is now caused to pass through the main portion of the tubebetween electrodes 4 and 5 and the single electrode '7. The potentialwhich is applied between either of the electrodes 4 and 5 and electrode7 is normally insufiicient to create a discharge therebetween but isgreat enough to maintain such a discharge when it is initiated byauxiliary means. Any means well known to the art may be used, such as ahigh frequency generator or other device for creating an instantaneoushigh potential between the two electrodes. Because the electrodes 4 and5 are heated to the point of producing electrons they will of necessityeach act as a cathode with respect to the electrode '7. The devicetherefore operates in full wave manner utilizing both alternations ofthe supply current cycle, the current passing alternately from theelectrode 7 to the electrodes 4 and 5. The choke coil 17 functions inthe usual manner to smooth out the flow of current from the tube.

The auxiliary circuit connection between the transformer and the mercuryelectrode 9 causes a quantity of this mercury to be vaporized anddiffused through the gas within the main portion of the envelope 1. Byadjusting the value of the resistance, the amount of mercury vapor maybe controlled. This general principle is more fully set forth in mycopending application Serial No. 343,873, filed March 2, 1929. Thisvapor, as stated before, passes down into the main bed of the envelope,and is energized by the passage of the main discharge currenttherethrough, with the result that the light emitted by the tube is acombination of that characteristic of the gas filling plus thatcharacteristic of mercury vapor. Where the gas used is neon theresultant light will be a combination of neon red and mercury blue. Byadjusting the resistance the color of the emitted. light may be variedbetween the pure neon red and the substantially pure mercury blue. Inthe latter case, the mercury may be made entirely to mask the lightproduced by the neon. By properly adjusting the resistance 18 theproduced light may be made white in appearance. I have found that wherea tube is used at 11 of relatively small size and great length that aneven diffusion of the mercury vapor through the discharge path of theelectrodes 4 and 5 and cooperating electrodes 7 is not had. This effectmay be overcome by providing small apertures or breather holes 12 whichin some manner permit the mercury vapor to permeate the entire length ofthe gaseous discharge path so that light of even color is produced theentire length of the tube.

I find that successful results may be obtained by utilizing at 1 anenvelope having a length of approximately 52" and a bore in theneighborhood of 18 mm., the distance between the electrodes 4 and 5being about 6" and the tube being filled with neon gas at a pressure ofabout 1 /2 mm. of mercury. With these dimensions the electrodes 4 and 5,may be of tungsten about five thousandths of an inch thick and having anarea of approximately one square inch. An alkali metal anode is used at7. The tube 11 may be 1 /2" long and have a bore of about 11 mm.

A tube thus designed will produce excellent results when the potentialof the transformer secondary 15 is approximately 600 volts, in whichcase the current through the main discharge path of the tube will be ofthe order of 10 amperes. when the resistance 18 is so regulated that I:the light produced is between neon red and mercury blue in color. Whilethe'pressure of neon gas within a tube of this length may be as low as 1/2 mm., when a shorter tube is used higher pressures are necessary forbest results. As stated above, I prefer to use thin tungsten electrodeswhich are so proportioned as to be heated to incandescence uponapplication of normal discharge current, but other electrodes may beused. For example, tungsten, or other metal, may be coated with some ofthe well known electron emitting materials in which case they could bearranged to operate at much lower temperatures and still produce thenecessary electron fiow.

What I claim is:

1. In an alternating current electrical discharge device, a gas filledenvelope containing a pair of tungsten electrodes and an associatedalkali metal electrode, means for applying a potential between saidtungsten electrodes sufiicient to beat them to incandescence and forcausing a current to flow between said alkali electrode and said pair ofelectrodes.

2. In an alternating current arrangement comprising an electricaldischarge device, a gas filled envelope, a pair of metallic electrodesof low thermal capacity within one end of said envelope and spacedapart, a third electrode containing alkali metal within said envelope,said electrode being of relatively high thermal capacity and spaced fromsaid pair of electrodes a distance greater than the spacing of theelectrodes constituting said pair, a mercury pool, said mercury beingadapted to be vaporized in small quantities and said vapor being adaptedto be mixed with said gas to modify the color of the light radiatedtherefrom.

3. An arrangement in accordance with claim 2 wherein means is providedfor passing a current between said pair of electrodes, and between eachof said pair of electrodes and said third electrode.

a. In an electrical discharge device, an envelope containing a rare gasand a quantity of mercury, an electrode chamber at one end of saidenvelope, a tube of smaller diameter than said envelope sealed to saidenvelope and projecting within said chamber, and a plurality of breatherholes in said tube adjacent to its point of juncture with said envelope.

5. In an alternating current electrical discharge arrangement, a gasfilled envelope, 2. pair of thermionic electrodes within said envelopeand spaced apart, a third electrode within said envelope and spaced fromsaid pair of electrodes a greater distance than the spacing of theelectrodes constituting said pair, a transformer having its secondaryterminals connected to said pair of electrodes and a connection from apoint between said terminals to said third electrode, the potential ofsaid transformer being suificient to cause said thermionic electrodes toemit electrons.

6. In an alternating current electrical discharge arrangement, a gasfilled envelope, a pair of thermionic electrodes within said envelopeand spaced apart, a third electrode of alkali metal within said envelopeand spaced apart from said pair of electrodes a greater distance thanthe spacing of the electrodes constituting said pair.

'I. An alternating current electrical discharge arrangement comprisingan envelope filled with neon gas, means for adding a quantity of mercuryvapor thereto, a pair of thermionic electrodes within said envelope andspaced apart, a third electrode within said envelope and spaced fromsaid pair of electrodes a greater distance than the spacing of theelectrodes constituting said pair.

CHARLES SPAETH.

